This is probably a dumb question but here it goes . will the base plate from a 650 dp work on a 600dp main body?

 

Yes, but it's not a direct swap. All the idle/tslot holes line up, but the 650 throttle plates will hit the lower opening of the venturis in the main body. You have to blend the lower 1" or so to match the 1-11/16 baseplate bores. The only difference in the 600 and 650 is throttle bore size, both use the same main body casting.

 

The 4776 Holley 600 dp has a baseplate with 1-9/16" bores. The 650 has 1-11/16" base plate bores. Both carbs use the same 1-1/4 primary and 1-5/16 secondary venturi. Like catherder said there will be a 1/16" step from the bottom of the venturi into the base plate.

Sometimes this isn't a problem, sometimes it messes with the signal at the transfer slot. The step can create turbulence across the transfer slot and cause some funky behavior.